Optical disk having clamp portion higher than substrate

ABSTRACT

A magneto-optical disc is prepared so as to have substrates made from polycarbonate, on which recording layers are formed so as to serve as signal recording medium sections facing to each other via a spacer. The magneto-optical disc is also provided with a clamp portion formed in such a way that when the magneto-optical disc is mounted on an optical disc recording and/or reproduction apparatus having an objective lens with a focal distance L 0 , the recording layer is positioned at a distance L 1  which is equal to a focal distance of the objective lens obtained in the substrate via reflection.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical disc such as an optical disc and a magneto-optical disc onto/from which a data is written or read out by an optical disc recording/reproduction apparatus.

[0003] 2. Description of the Prior Art

[0004] An optical disc including a magneto-optical disc has been suggested for saving a data of audio, video, or computer. This optical disc, for example, has a recording section on a transparent substrate and a data is recorded on this recording section.

[0005] For example, as shown in FIG. 1, a magneto-optical disc having a signal recording plane only on one side is formed from a disc-shaped transparent resin such as polycarbonate including: a substrate 102 having a thickness of, for example, about 1.2 mm; a recording layer 103 formed on the substrate 102; and a protection layer 104 formed on the recording layer 103. This magneto-optical disc 101 is an optical disk normalized by the International Standard Organization (ISO) such as ISO/IEC 10089 and 13549 and enables data writing by forming the recording layer 103 from a magnetized film. The magneto-optical disc 101 has a clamp portion 105 at the center portion.

[0006] Moreover, an optical disc recording and/or reproduction apparatus which enables to write or read a data onto/from the magneto-optical disc 101 includes: a clamp 106 for holding a hub (not depicted) provided in the clamp portion 105 of the magneto-optical disc 101 mounted and for rotating the magneto-optical disc 101; and an objective lens 107 for focusing a laser beam emitted from a light source (not depicted) on the recording layer 103. The objective lens 107 and the clamp 106 are arranged at positions matching the configuration of the magneto-optical disc mounted on the optical disc recording and/or reproduction apparatus.

[0007] For example, the objective lens 107 is supported in such a manner that it can move within a predetermined stroke for focus servo. The objective lens 107 is positioned at a neutral position (position X₁ in FIG. 1) of the focus servo for the magneto-optical disc 101.

[0008] The optical disc recording and/or reproduction apparatus having such configuration writes or reads out a onto/from the magneto-optical disc 101.

[0009] Here, the magneto-optical disc can increase a data recording density by decreasing the thickness of the substrate as shown in FIG. 2. It should be noted that FIG. 1 and FIG. 2 show a single-sided type magneto-optical disc, but a so-called double-sided magneto-optical disc is said to be able to further increase a data recording density.

[0010] It has bee desired to provide an optical disc recording and/or reproduction apparatus capable of recording or reproducing a data onto/from both of the magneto-optical disc 101 having a conventional substrate thickness of about 1.2 mm and a magneto-optical disc 109 which is said to enable a higher recording density by reducing a substrate thickness. That is, an apparatus compatible for both of the discs is desired.

[0011] In this case, it is considered to design the compatible optical disc recording and/or reproducing apparatus so as to match with, for example, the conventional magneto-optical disc 101. For example, if the objective lens 107 is subjected to a focus servo when a magneto-optical disc is mounted, a data can be recording or reproduced onto/from both of the magneto-optical discs 101 and 109.

[0012] However, if it is impossible to obtain a stroke (a distance between X₁ and X₂ in FIG. 2) required for carrying out a focus servo to the magneto-optical disc 109, the optical disc recording and/or reproduction apparatus cannot carry out focusing.

[0013] Furthermore, if focus is obtained at a shift limit position of the objective lens 107 during a focus servo, focus characteristic is deteriorated because the objective lens 107 is not positioned at a neutral position for carrying out an appropriate focusing.

[0014] Moreover, in order to provide a greater shift stroke for the objective lens 107, the optical disc recording and/or reproduction apparatus should have an additional function.

SUMMARY OF THE INVENTION

[0015] It is therefore an object of the present invention to provide an optical disc onto which focus can be obtained with the same objective lens even if the substrate thickness varies.

[0016] The optical disc according to the present inveniton includes: a transparent substrate; a recording layer formed on the transparent substrate; and a clamp portion provided at a center portion of the transparent substrate; the clamp portion and the transparent substrate having surfaces different in height so that the recording layer plane is positioned in the vicinity of focus position of the objective lens which is at a neutral position.

[0017] According to another aspect of the inveniton, the optical disc has a higher recording density than a normalized optical disc, and includes: a transparent substrate having a smaller thickness than the normalized optical disc; a recording layer formed on the transparent substrate; and a clamp portion which has a thickness identical to that of the normalized optical disc and is rotatably suported by a clamper provided in an optical disc recording and/or reproduction apparatus.

[0018] The optical disc having the aforementioned configuration enables to minimize the stroke of the objective lens provided in the optical disc recording and/or reproduction apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 shows configuration of a conventional magneto-optical disc.

[0020]FIG. 2 shows configuration a conventional magneto-optical disc which requires shifting of a lens.

[0021]FIG. 3 is a cross-sectional view showing a disc rotation drive block for rotating the aforementioned magneto-optical disc.

[0022]FIG. 4 is a plan view of a magneto-optical disc according to the present invention.

[0023]FIG. 5 shows configuration of the aforementioned magneto-optical disc.

[0024]FIG. 6 shows configuration of an essential portion of the aforementioned magneto-optical disc.

[0025]FIG. 7 shows configuration of a magneto-optical disc according to another embodiment of the present invention.

[0026]FIG. 8 is a perspective view showing the aforementioned magneto-optical disc contained in a disc cartridge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Description will now be directed to preferred embodiments of the present invention with reference to the attached drawings.

[0028] That is, explanation will be given on a magneto-optical disc onto/from which a data can be written or read out by applying a laser beam through an objective lens provided in an optical disc recording and/or reproduction apparatus.

[0029] Here, the optical disc recording and/or reproduction apparatus is a so-called compatible optical disc recording/or reproduction apparatus capable of writing and reading out a data onto/from magneto-optical discs having different substrate thicknesses, for example, a magneto-optical disc having a substrate thickness of about 0.6 mm and a magneto-optical disc having a substrate thickness of about 1.2 mm.

[0030] The aforementioned optical disc recording and/or reproduction apparatus includes: a rotation drive block to be matched with a clamp portion formed at the rotation center of the magneto-optical disc, so as to rotate the magneto-optical disc; and an objective lens for focusing a laser beam on a signal recording plane of the magneto-optical disc.

[0031] The aforementioned objective lens and the clamp are arranged in an optical disc recording and/or reproduction apparatus so as to match with the conventional magneto-optical disc having a substrate thickness of about 1.2 mm. More specifically, the objective lens is positioned at a neutral position, i.e., at an intermediate position of focus servo carried out for the magneto-optical disc having the substrate thickness of about 1.2 mm.

[0032] The disc rotation drive block serves to rotate the aforementioned magneto-optical discs and as shown in FIG. 3, includes: a damper 41 formed so as to match with a hub provided on the magneto-optical disc which will be detailed later; a spindle shaft 42 which thrusts through and supports the damper 41; and a spindle motor for rotating this spindle shaft 42. The damper is formed approximately into a cylindrical shape having one end open and has a magnet 44 formed into a ring shape at the bottom of the damper 41. This disc rotation drive block 40 is arranged in the optical disc recording and/or reproduction apparatus in such a manner that the damper 41 is properly matched with the normalized magneto-optical disc having the substrate thickness of 1.2 mm.

[0033] Hereinafter, explanation will given on a so-called double-sided magneto-optical disk having a signal recording plane on both sides, whereas the magneto-optical disk having the substrate thickness of 1.2 mm will be referred to as the other type of magneto-optical disc.

[0034]FIG. 4 is a plan view showing the aforementioned magneto-optical disc having a substrate thickness of 0.6 mm. As shown in FIG. 4, the magneto-optical disc has a disc shape consisting of a recording area where a data signal is recorded; a control track 3 positioned at the inner circumference of this recording area for containing data such as sector length and modulation method; and a control track 4 positioned at the inner circumference of the recording area 2 and a control track 5 positioned at the outer circumference of the recording area 2 for containing a data such as recording and erase conditions.

[0035] As shown in FIG. 5, the magneto-optical disc 1 having the aforementioned control tracks 3, 4, and 5, and the recording area 2 consists of a first signal recording medium section 13 including a substrate 11 and a recording layer 12 formed on the substrate 11 and a second signal recording medium section 14 consisting of a substrate 11 and a recording layer 12 formed on the substrate 11. The first signal recording medium section 13 and the second signal recording medium section 14 are arranged with their recording layers facing to each other, while sandwiching a spacer 15. Thus, the magneto-optical disc 1 has a signal recording plane on both sides.

[0036] The aforementioned substrate 11 is made from a transparent resin material such as polycarbonate having a thickness of 0.6 mm.

[0037] The aforementioned recording layer 12 is made from a magnetized film enabling a data write. For example, when a data is recorded, a laser having a power adjusted for a data write is applied from the optical disc recording and/or reproduction apparatus and the magnetization direction is changed by the magnetic head, thus writing a data on the recording layer 12.

[0038] The aforementioned spacer 15 is made from, for example, a transparent resin material such as polycarbonate in the same way as the substrate 11.

[0039] The magneto-optical disc 1 has the aforementioned clamp portion 16 formed at the center portion. This clamp portion 16 has an upper surface 16 a formed higher than a substrate surface 11 a so that the recording layer 12 is positioned at the neutral position when focused by the objective lens. Hereinafter, detailed explanation will given on a forming position of this substrate surface 11 a.

[0040] As shown in FIG. 6, when the magneto-optical disc 1 is mounted on the optical disc recording and/or reproduction apparatus, the objective lens 51 has a natural focal distance L₀ which is changed to a distance L₁ because an incident light from the substrate surface 11 a is reflected. That is, the focal distance is changed so that the incident light is focused on the recording layer 12 at approximately 0.6 mm from the substrate surface 11 a. In other words, the magneto-optical disc 1 is held by the damper 41 so that the substrate surface 11 a is located at a proper position for the neutral position of the objective lens 51, thus enabling focus on the recording layer 12. Here, the damper 41, as has been described above, is arranged so that the clamp portion of the aforementioned the other type of magneto-optical disc can be properly mounted. However, the magneto-optical disc 1 is sure to be mounted on this damper 41 by the clamp portion surface 16 a positioned at a protruding position from the substrate surface 11 a.

[0041] The magneto-optical disc 1 has such a clamp portion surface 16 a formed on both sides of the disc. Moreover, the magneto-optical disc 1 adjusts a distance between the two clamp portion surfaces 16 a and 16 a by the thickness of the spacer 15 formed to approximately 2.4 mm so that the distance will be identical to the thickness of the other type of magneto-optical disc 26 which will be detailed below.

[0042]FIG. 7 shows configuration of the other type of magneto-optical disc having a normalized substrate thickness of 1.2 mm with a recording plane on both sides. This magneto-optical disc includes two signal recording medium sections 24 and 25, each consisting of a substrate 21; a recording layer 22 formed on the substrate 21; and a protection layer 23 formed on the recording layer 22.

[0043] As shown in FIG. 7, the aforementioned damper 41 and the objective lens 51 are arranged to match with the other type of the magneto-optical disc 26 so that a clamp portion 27 has a clamp portion surface 27 a forms a single plane with a substrate surface 27 a without any step.

[0044] That is, the damper 41 and the objective lens 51 are arranged in such a manner that when the other type of magneto-optical disc 26 is mounted on the damper 41, the objective lens 51 has a natural focal distance L₀ which is changed by reflection in the substrate 21 to a focal distance L₂, enabling to focus on the recording layer 22.

[0045] It should be noted that the other type of the magneto-optical disc has a clamp portion surface 27 a on its both sides. Moreover, the other type of magneto-optical disc is formed so as to have the clamp portion with a thickness of approximately 2.4 mm which is also the distance between the two substrate surfaces 21 a and 21 a.

[0046] Thus, the magneto-optical disc 1 and the other type of magneto-optical disc 26 can be focused by the objective lens 51 having an identical neutral position.

[0047] Moreover, each of the magneto-optical discs 1 and 26 is provided with a hub which is coaxial with the clamp portion. For example, as shown in FIG. 4 and FIG. 5, the hub is formed approximately into a cylindrical form so that the damper 41 of the disc rotation drive block 40 can be attached and removed to/from the hub. That is, the hub 31 has an outer diameter which is slightly smaller than the inner diameter of the damper 41. Moreover, the hub 31 is provided with a magnetic metal member 32 formed into a rig shape and attached at the both ends of the hub 31. The hub 31 is also has a through hole 31 a into which the spindle shaft 42 of the disc rotation drive block 40 is inserted.

[0048] Each of the aforementioned magneto-optical discs 1 and 26 is surely held by the disc rotation drive block 40 via the hub formed as described above.

[0049] Each of the magneto-optical discs 1 and 26 having the above described configurations is rotatably contained in a disc cartridge 34 having a cartridge body 33 formed approximately into a thin square type box. This disc cartridge 34 has: a magnetic head advance opening 35 allowing a magnetic head of the optical disc recording and/or reproduction apparatus to access the recording area 2 of the magneto-optical disc contained in the cartridge body 33; a disc rotation drive block advance opening 36 allowing the damper 41 of the disc rotation drive block 40 be mounted on the hub 31 of the magneto-optical disc 1, 26; a shutter 37 which is slidably supported on the cartridge body 33 for covering the magnetic head advance opening 35 and the disc rotation drive block advance opening 36; identifier holes 38 a and 38 b for identifying information of the signal recording medium sections of the magneto-optical disc 1, 26; and a positioning hole 39 for positioning the cartridge when inserted into the optical disc recording and/or reproduction apparatus.

[0050] The disc cartridge 34 also serves to prevent adhesion of dusts to the signal recording medium sections of the magneto-optical disc 1 and 26 when contained in the disc cartridge 34. When the disc cartridge is mounted on the optical disc recording and/or reproduction apparatus (not depicted) for recording or reproduction, the magneto-optical disc 1 or the other type of magneto-optical disc 26 is mounted on the disc rotation drive block 40 as described above.

[0051] For example, when a data is to be written onto the magneto-optical disc 1, focusing can be carried out with the objective lens 51 whose neutral position is almost identical to the case when the other type of magneto-optical disc 26 is mounted.

[0052] That is, the optical disc recording and/or reproduction apparatus can obtain a sufficient stroke for focus servo from the neutral position of the objective lens, enabling to prevent deterioration of the focus servo characteristic.

[0053] Thus, the magneto-optical disc 1 having the clamp portion 16 can be arranged in the optical disc recording and/or reproduction apparatus having the objective lens 51 with its focus position adjusted for the other type of magneto-optical disc 26, without changing the focus servo stroke. Consequently, the optical disc recording and/or reproduction apparatus need not provide a particular function for coping with the magneto-optical discs having different substrate thicknesses, thus enabling to suppress increase of the apparatus size as well as production costs.

[0054] Moreover, as focusing can be carried out at the same position without moving the objective lens 51 according to the type of the magneto-optical disc, this brings about a great advantage for an optical disc recording and/or reproduction apparatus which, for example, reads a signal recording plane of a magneto-optical disc mounted so as to identify the type of the magneto-optical disc.

[0055] It should be noted that the clamp portion surface 16 a of the magneto-optical disc 1 can also be formed as indented from the surface 11 a of the substrate 11. For example, this can be applied when the magneto-optical disc 1 has a substrate thickness greater than that of the other type of the magneto-optical disc 26.

[0056] Moreover, the magneto-optical disc 1 may have the clamp portion 16 having the protruding portion 16 b made from another material, for example, a material having a mechanically superior strength. In such a case, the magneto-optical disc 1 can increase the strength against shock applied when mounting and removing the damper 41.

[0057] Furthermore, the magneto-optical disc 1 is not limited to the aforementioned double-sided disc but can also be applied to a so-called single-sided disc having a signal recording plane on one side.

[0058] The magneto-optical disc according to the present invention has a clamp portion surface and a transparent substrate surface which are different in height so that the recording layer plane is at a focus position of the objective lens at a neutral position. This enables to carry out focus servo at the same position without changing the position of the objective lens according to magneto-optical discs having different substrate thicknesses. Consequently, the optical disc recording and/or reproduction apparatus need not have a particular function for focusing on the aforementioned magneto-optical disc. 

What is claimed is:
 1. An optical disc onto/from which a data is written or read out by a laser beam applied via an objective lens provided in an optical disc recording and/or reproduction apparatus, said optical disc comprising: a transparent substrate; a recording layer formed on said transparent substrate; and a clamp portion provided at a center portion of said transparent substrate; said clamp portion and said transparent substrate having surfaces different in height so that said recording layer plane is positioned in the vicinity of focus position of said objective lens which is at a neutral position.
 2. An optical disc as claimed in claim 1, said disc is a double-sided disc having two of said transparent substrates and two of said recording layers facing to each other sandwiched by said two transparent substrates.
 3. An optical disc as claimed in claim 2, said double-sided disc having a clamp portion with thickness identical to a normalized optical disc thickness.
 4. An optical disc having a higher recording density than a normalized optical disc, said optical disk comprising: a transparent substrate having a smaller thickness than said normalized optical disc; a recording layer formed on said transparent substrate; and a clamp portion which has a thickness identical to that of said normalized optical disc and is rotatably supported by a damper provided in an optical disc recording and/or reproduction apparatus.
 5. An optical disc as claimed in claim 4, wherein a distance between a surface of said clamp portion and said recording layer is defined so that a focus point is positioned on said recording layer when said clamp portion is supported by said damper provided in said optical disc recording and/or reproduction apparatus.
 6. An optical disc as claimed in claim 4, said optical disc further comprising a spacer portion having a thickness defined so that said clamp portion has a thickness identical to that of said normalized optical disc.
 7. An optical disc as claimed in claim 6, wherein said recording layer is formed at approximately 0.6 mm from the surface of said transparent substrate. 